This invention relates to an apparatus for machining or grinding a large and heavy workpiece, and more particularly to an apparatus of the aforesaid type which includes a rotatable tool support mounted for rotation on an in-place stationarily-mounted runner of a hydro-turbine machine. The apparatus includes a self-contained drive package for the tool support whereby the tool, such as a grinding wheel, may be bodily rotated to effect with the surface of the turbine wear ring while mounted on the turbine runner without being removed from the runner. The invention will be described in connection with the machining of the extremely heavy and large runner of a hydraulic turbine. Such a runner typically might have a weight of 450 tons, and a physical size such as 20 feet in diameter and a height of 12 feet.
The apparatus for machining a workpiece is particularly useful for use in machining an extremely large workpiece such as the runner of a hydraulic turbine, for example, which is too large and heavy for construction and machining in one piece at a manufacturing site which may be far distant from the site of its intended use, and which therefore requires that a plurality of pieces manufactured at the factory be fabricated into a unitary member in its operating position at the site of its intended use.